Liquid crystal display (LCD) is commonly used as a display device because of its capability of displaying images with good quality while using little power. An LCD apparatus includes an LCD panel formed with liquid crystal cells and pixel elements with each associating with a corresponding liquid crystal cell and having a liquid crystal capacitor and a storage capacitor, a thin film transistor (TFT) electrically coupled with the liquid crystal capacitor and the storage capacitor. These pixel elements are substantially arranged in the form of a matrix having a number of pixel rows and a number of pixel columns. Typically, scanning signals are sequentially applied to the number of pixel rows for sequentially turning on the pixel elements row-by-row. When a scanning signal is applied to a pixel row to turn on corresponding TFTs of the pixel elements of a pixel row, source signals (image signals) for the pixel row are simultaneously applied to the number of pixel columns so as to charge the corresponding liquid crystal capacitor and storage capacitor of the pixel row for aligning orientations of the corresponding liquid crystal cells associated with the pixel row to control light transmittance therethrough. By repeating the procedure for all pixel rows, all pixel elements are supplied with corresponding source signals of the image signal, thereby displaying the image signal thereon.
Liquid crystal molecules have a definite orientational alignment as a result of their long, thin shapes. The orientations of liquid crystal molecules in liquid crystal cells of an LCD panel play a crucial role in the transmittance of light therethrough. For example, in a twist nematic LCD, when the liquid crystal molecules are in its tilted orientation, light from the direction of incidence is subject to various different indexes of reflection. Since the functionality of LCDs is based on the birefringence effect, the transmittance of light will vary with different viewing angles. Due to such differences in light transmission, optimum viewing of an LCD is limited within a narrow viewing angle. The limited viewing angle of LCDs is one of the major disadvantages associated with the LCDs and is a major factor in restricting applications of the LCDs.
Several approaches exist for increasing the viewing angles of LCDs, such as in-plane switching (IPS), and fringe field switching (FFS). As shown in FIG. 9(a) an IPS mode LCD 910 has a structure that two pixel electrodes 921 and a common electrode 929, both for driving liquid crystal molecules 932, are formed on a first substrate 920 in parallel. When a voltage is applied to the pixel electrodes 921 and the common electrode 929, an electric field 937 is generated in-plane to the surface of the first substrate 920. In the IPS mode LCD 910, a distance, L1, defined between the common electrode 929 and the pixel electrode 921 is about the same order as a cell gap, d1, defined between the first substrate 920 and the second substrate 940. The IPS mode LCD 920 has the advantage of viewing angle that is wider than the conventional TN mode LCD. However, since the pixel and the common electrodes 921 and 929 are made of opaque metal films, there is a limitation in aperture ratio and transmittance of light 945. In addition, due to the planar electric field structure, the IPS mode LCD inherently suffers from severe image sticking.
In order to overcome the limitation of the IPS mode LCD in aperture ratio and transmittance of light, an FFS mode LCD is introduced. In the FFS mode LCD 950, as shown in FIG. 9(b), a plurality of pixel electrodes 961 and a common electrode 969 are made of transparent metal films, for example, indium tin oxide metal films, thereby improving the aperture ratio compared to the IPS mode LCD. Furthermore, a distance, L2, defined between two pixel electrodes is narrower than that a cell gap, d2, defined between the first substrate 970 and the second substrate 990. When a voltage is applied between the pixel electrodes 961 and 969, a fringe field 981 is generated in a region of the cell gap adjacent to the common and the pixel electrodes 961 and 969, liquid crystal molecules 982 disposed within the region are all driven, thereby improving the transmittance of light 995, comparing to the IPS mode LCD.
However, in the IPS mode LCD and the FFS mode LCD, no conductive metal films are formed on the second substrate for preventing distortion of the electric field generated by the pixel electrode and the common electrode on the first substrate. Usually, an ITO film is formed on the back side of the second substrate to protect the LCD from electro-static damage, which makes increase manufacture cost and material cost of a color filter.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.